Radius end mill

ABSTRACT

In the radius end mill, main gash faces has an angle of inclination with respect to an axis that is smaller than a twist angle of chip discharge flutes. The main gash faces are formed on inner circumferential sides of distal end portions of wall surfaces that face in a tool rotation direction of helically twisted chip discharge flutes, which is formed on an outer circumference of a distal end portion of a tool body that is rotated around the axis. End cutting edges are formed on a distal end of the main gash faces. Sub gash faces has an angle of inclination with respect to the axis that is greater than that of the main gash faces. The sub gash faces are formed on an outer circumferential side of the main gash faces such that they extend away via step portions from the main gash faces. In addition, corner cutting edges that have a protruding arc-shaped contour are formed to be continuous with an outer circumferential side of the end cutting edges extending from a distal end as far as an outer circumference of the sub gash faces.

TECHNICAL FIELD

The present invention relates to a radius end mill that is used to cut awork piece such as, for example, a metal die.

BACKGROUND OF THE INVENTION

An example of a radius end mill that is used in the machining of a workpiece in which a corner cutting edge, in which an end cutting edge and aperipheral cutting edge intersect, is formed in a convex arc shape isdisclosed in Japanese Unexamined Patent Application, First PublicationNo. S59-175915.

As is shown in FIG. 31, in this radius end mill there is provided an endmill in which end cutting edges 2 are positioned at a distal end of atool body 1 and peripheral cutting edges 3 are positioned at apredetermined twist angle θ₁ on an outer circumference of the tool body1. In this end mill, a twist angle θ₂ of corner cutting edges 4 in thevicinity of a corner of the edge tip is smaller than the twist angle θ₁of the peripheral cutting edges 3 that are connected to the cornercutting edges 4. In addition, a corner R is provided on the cornercutting edges 4. In this type of radius end mill, because the smalltwist angle θ₂ is provided in the vicinity of a distal end of the cornercutting edges 4, the edge tip corner does not form an extremely acuteangle, and working of the corner R is simplified while accuracy may bemaintained. In addition, there are no defects in the edge due to thethinness of the edge tip corner portion. Moreover, because the portionsof the peripheral cutting edges 3, which are the centers of themachining, are provided with a large twist angle θ₁, which has excellentmachining properties, materials that are difficult to machine such astitanium alloys and stainless steel may be machined easily and with ahigh degree of accuracy. Furthermore, it is possible to achieve a markedimprovement in reducing tool costs and in the processing efficiency ofthe milling tasks.

However, in this radius end mill, because the twist angle θ₂ of thecorner cutting edges 4, which are provided with a corner R, on thedistal end side of the peripheral cutting edges 3 is made weak, namely,because the rake angle in the axial direction of the corner cuttingedges 4 and the end cutting edges 2 that are connected to the cornercutting edges 4 and extend to the inner circumferential side is small,although the included angle of the end cutting edges 2 and cornercutting edges 4 may be enlarged and it is possible to prevent defects,as is described above, it is not possible to prevent the blunt. Whereas,if, for example, the depth of a cut is shallow, and the center of thecut is not on the peripheral cutting edge 3 side but is on the endcutting edge 2 side, then because the distance from the center axis O ofthe tool body 1 is short on the inner peripheral side of the end cuttingedges 2, the cutting speed is slow. Accordingly, the load during thecutting is increased and greater edge tip strength is required. Incontrast, because the cutting speed is fast at the corner cutting edges4 on the outer peripheral side of the end cutting edges 2, the loadduring the cutting is light, and, instead of greater edge tip strength,what is required is a sharp cutting edge. However, in a radius end millin which the axial direction rake angle is small extending from the endcutting edges 2 to the corner cutting edges 4, in the manner describedabove, on the contrary, there is a possibility that there will be anincrease in the cutting resistance.

Moreover, in particular, if a slanted metal surface or curved metalsurface is cut using this type of radius end mill, because a number ofthe corner cutting edges 4 that are provided with the corners R in thevicinity of the edge tip corners thereof are used, if the sharpness ofthe edges in portion such as this is poor and there is considerablecutting resistance, then there is no possibility of achieving animprovement in the processing efficiency. Furthermore, in the abovedescribed conventional radius end mill, because the peripheral cuttingedges 3 that are connected to the corner cutting edges 4 are providedwith twist angle gradual increase portions 5 that extend from the twistangle θ₂ to the large fixed twist angle θ₁ so that the twist angle ismade to change gradually, and because, in conjunction with this, therake faces that are continuous with the cutting edges 4 are also formedas smoothly continuous faces whose incline gradually changes, shavingsthat are produced by the corner cutting edges 4 are discharged in anelongated form along these rake faces, and the problem also arises thatthere is a deterioration in the ability to process these chips.

Furthermore, FIG. 32 is an enlarged view showing principal portions ofthis conventional radius end mill. Corner portions 6, which are convexon the corner cutting edge 4 side, are formed on rake faces 2A and 4A asa result of an inner edge 2B (i.e., a boundary line between the rakeface 2A and a wall face that protrudes outwards on the front side in therotation direction T of the tool from the rake face 2A) of the rake face2A of the end cutting edge 2 and an inner edge 4B (i.e., a boundary linebetween the rake face 4A and a wall face that protrudes outwards on thefront side in the rotation direction T of the tool from the rake face4A) of the rake face 4A of the corner cutting edge 4 intersecting at anobtuse angle.

However, in this type of radius end mill, a shortening of the intervalfrom the end cutting edges 2 and corner cutting edges 4 to the inneredges 2B and 4B that corresponds to the size of the corner portions 6,which are intersecting portions between the inner edges 2B of the rakefaces 2A of the end cutting edges 2 and the inner edges 4B of the rakefaces 4A of the corner cutting edges 4, may not be avoided. Inconjunction with this, because it also becomes impossible to ensure asufficiently large space for the discharging chips, the problem arisesthat there is deterioration in the ability to discharge the chips.

In particular, in a radius end mill in which a ratio r/D between aradius of curvature “r” of substantially arc-shaped portions formed bythe corner cutting edges 4, which constitute the intersection portions(i.e., corner portions) between the peripheral cutting edges 3 and theend cutting edges 2, and a diameter D of the tool body 1 is set to 0.2or more, or in a radius end mill in which the radius of curvature “r” ofthe substantially arc-shaped portions formed by the corner cutting edges4 is set to (D−d)/2 or more with respect to the diameter D and the webthickness “d” of the tool body 1, because the corner cutting edges 4 areenlarged and there is a tendency for the interval from the end cuttingedges 2 and corner cutting edges 4 to the inner edges 2B and 4B to bereduced, the above described problem of there being a deterioration inthe ability to discharge the chips is conspicuous.

Moreover, in the corner portions 6 in which the inner edges 2B and 4Bintersect with each other, the chips easily become caught up and thepresence of the corner portions 6 causes a further deterioration in theability to discharge the chips.

DISCLOSURE OF INVENTION

The present invention was conceived from this background and it is anobject thereof to provide a radius end mill that enables a high degreeof sharpness to be imparted to a protruding arc-shaped corner cuttingedge that has a corner R provided on an outer circumferential sidethereof, while enabling sufficient edge tip strength to be secured onthe inner circumferential side of an end cutting edge, and that alsoachieves an improvement in the ability to dispose of chips produced bythis corner cutting edge.

In order to achieve these objects, in the present invention, chipdischarge flutes that are helically twisted are formed on an outercircumference of a distal end portion of a tool body that is rotatedaround an axis, main gash faces whose angle of inclination with respectto the axis is a smaller angle than a twist angle of the chip dischargeflutes are formed on inner circumferential sides of distal end portionsof wall surfaces of the chip discharge flutes that face in the directionof rotation of the tool; and the end cutting edges are formed on adistal end of the main gash faces, and sub gash faces whose angle ofinclination with respect to the axis has been made greater than that ofthe main gash faces are formed on an outer circumferential side of themain gash faces such that they extend away via step portions from themain gash faces. In addition, the corner cutting edges that have aprotruding arc-shaped contour are formed so as to be continuous with anouter circumferential side of the end cutting edges from a distal end asfar as an outer circumference of the sub gash faces.

Accordingly, in a radius end mill that is structured in this manner,because main gash faces that are inclined with respect to the axis at asmaller angle than the twist angle of the chip discharge flutes areformed on inner circumferential sides of distal end portions of the chipdischarge flutes, and because end cutting edges are formed on the distalends thereof, the included angle of the end cutting edges may beincreased, and it is possible to secure a cutting edge strength that issufficient to withstand a large cutting load such as that describedabove. In addition to this, because sub gash faces whose angle ofinclination with respect to the axis has been made greater than that ofthe main gash faces are formed on an outer circumferential side of themain gash faces and protruding arc-shaped corner cutting edges areformed on outer circumferential portions of the distal end of the subgash faces, the rake angle in the axial direction of these cornercutting edges may be made larger than that of the end cutting edges, sothat they are provided with excellent sharpness. Moreover, because thesub gash faces that are continuous with the corner cutting edges andform the rake faces thereof are made to extend away via step portionsfrom the main gash faces that form the rake faces of the end cuttingedges, and because, as a result of this, the chips that are produced bythe corner cutting edges may be made to collide against these stepportions, resistance may be imparted to the chips before they aredischarged in an elongated shape, so as to curl or break them, therebyimproving the ability to dispose of the chips.

However, if the step portions between the main gash faces and the subgash faces are formed, for example, so as to be perpendicular to the subgash faces, then the chips that are produced by the corner cutting edgesas is described above create blockages when they collide against thesestep portions, so that the chip discharge performance is deterioratedand, conversely, there is a possibility that the smooth disposal of thechips will be obstructed. Therefore, it is desirable that the stepportions be formed as inclined surfaces that move gradually away as theymove from the main gash face side towards the sub gash face side.

Moreover, it is desirable that an angle of inclination of the inclinedsurfaces formed by the step portions in this case be within a range of30° to 60° with respect to a direction that is perpendicular to the subgash faces. If this angle of inclination is less than 30° and the risein the step portions is a steep gradient, then there is a possibilitythat it will not be possible to sufficiently prevent the aforementionedblockages of chips from occurring. If, on the other hand, theinclination is a gentle slope that exceeds 60°, then the possibilityarises that it will not be possible to impart sufficient resistance tocollided chips and achieve reliable disposal.

Furthermore, when the step portions are formed as inclined surfaces inthis manner, these inclined surfaces may be planar surfaces that have aconstant angle of inclination, however, if the inclined surfaces areformed as concave curved surfaces, it becomes easier to curl thecollided chips and more reliable chip disposal may be achieved.

A further object of the present invention is to provide a radius endmill that enables chips to be disposed of in an excellent manner.

In order to achieve this object, in the present invention, in a radiusend mill in which end cutting edges and substantially arc-shaped cornercutting edges are formed on a tool body that is rotated around an axis,inner edges of rake faces of the end cutting edges and inner edges ofrake faces of the corner cutting edges are formed as a single, smoothlycontinuous convex curve.

In the present invention that is constructed in this manner, becauseinner edges of rake faces of the end cutting edges and inner edges ofrake faces of the corner cutting edges are formed as a single, smoothlycontinuous convex curve, and because, unlike the conventional structure,there are no corner portions produced by the inner edges intersectingeach other formed on these rake faces, it is possible to increase thespacings between the end cutting edges and the corner cutting edges andthe inner edges of the rake faces thereof by the amount obtained byobviating these corner portions. Namely, by securing a large enoughspace for discharging chips, it is possible to maintain an excellentchip disposal performance.

Furthermore, in the same manner, because the inner edges of the rakefaces of the end cutting edges and corner cutting edges together form asingle continuous convex curve, when produced chips are discharged, itis difficult for these chips to become caught, and the chips may bedischarged smoothly. Because of this as well, it is possible to maintainan excellent chip discharge performance.

It is also preferable that a rake face of an end cutting edge and a rakeface of a corner cutting edge are formed as a single, smoothlycontinuous curved surface. By forming a rake face of an end cutting edgeand a rake face of a corner cutting edge as a single, smoothlycontinuous curved surface, produced chips are able to pass smoothly overthese rakes faces, resulting in a further improvement in the chipdischarge performance being achieved.

The present invention enables a considerable effect to be expected incases such as when a ratio r/D between a radius of curvature “r” of thesubstantially arc shapes formed by the corner cutting edges and thediameter D of the tool body is set to 0.2 or more, or when the radius ofcurvature “r” of the substantially arc-shaped portions formed by thecorner cutting edges is set to (D−d)/2 for the diameter D and the corethickness “d” of the tool body, namely, in cases when the corner cuttingedges are large and it is necessary to have a small spacing between thecorner cutting edges and end cutting edges and the inner edges of therake faces of these edges.

BRIEF DESCRIPTION DRAWINGS

FIG. 1 is a plan view of a distal end portion of a tool body 11 showinga first embodiment of the present invention,

FIG. 2 is a side view of the embodiment shown in FIG. 1,

FIG. 3 is a front view as seen from the distal end in a direction of anaxis O of the embodiment shown in FIG. 1, and

FIG. 4 is a cross-sectional view taken along the line Z-Z in FIG. 1.

FIG. 5 is a plan view of a distal end portion of a tool body 11 showinga second embodiment of the present invention,

FIG. 6 is a side view of the embodiment shown in FIG. 5,

FIG. 7 is a front view as seen from the distal end in a direction of anaxis O of the embodiment shown in FIG. 5, and

FIG. 8 is a cross-sectional view taken along the line Z-Z in FIG. 5.

FIG. 9 shows a third embodiment of the present invention, andcorresponds to the cross-sectional view taken along the line Z-Z in FIG.5.

FIG. 10 is a plan view showing a fourth embodiment of the presentinvention,

FIG. 11 is a cross-sectional view of a distal end portion (i.e., across-sectional view taken along the line Y-Y in FIG. 12) of a tool body11 of the embodiment shown in FIG. 10, and

FIG. 12 is a front view as seen from the distal end in a direction of anaxis O of the embodiment shown in FIG. 10.

FIG. 13 to FIG. 15 show an indexable insert 33 that is mounted on theembodiment shown in FIG. 10, and FIG. 13 is a plan view, FIG. 14 is aside view, and FIG. 15 is a front view.

FIG. 16 and FIG. 17 show a clamp mechanism 34 of the embodiments shownin FIGS. 10 and 25, and FIG. 16 is a cross-sectional view taken alongthe line Z-Z in FIGS. 10, 12, 25, and 27, and FIG. 17 is across-sectional view taken along the line Z-Z in FIG. 16 (the indexableinsert 33 and clamp screw 42 are omitted from the drawings).

FIG. 18 is a plan view of a radius end mill according to a fifthembodiment of the present invention,

FIG. 19 is a side view of a radius end mill according to the fifthembodiment of the present invention,

FIG. 20 is a view of a distal end surface of a radius end mill accordingto the fifth embodiment of the present invention, and

FIG. 21 is a cross-sectional view of a tool body 50 of a radius end millaccording to the fifth embodiment of the present invention.

FIG. 22 is a plan view of a radius end mill according to a sixthembodiment of the present invention,

FIG. 23 is a side view of a radius end mill according to the sixthembodiment of the present invention, and

FIG. 24 is a view of a distal end surface of a radius end mill accordingto the sixth embodiment of the present invention.

FIG. 25 is a plan view showing a seventh embodiment of the presentinvention,

FIG. 26 is a cross-sectional view of a distal end portion (i.e., across-sectional view taken along the line Y-Y in FIG. 27) of the toolbody 11 of the embodiment shown in FIG. 25,

FIG. 27 is a front view as seen from the distal end in the direction ofthe axis O of the embodiment shown in FIG. 25.

FIG. 28 to FIG. 30 show an indexable insert 60 that is mounted on theembodiment shown in FIG. 25, FIG. 28 is a plan view, FIG. 29 is a sideview, and FIG. 30 is a front view.

FIG. 31 is a plan view of a conventional radius end mill,

FIG. 32 is an enlarged view of principal portions of the conventionalradius end mill shown in FIG. 31.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will now be describedwith reference made to the drawings. It should be understood, however,that the present invention is not limited to these embodiments and, forexample, various combinations of component elements of the embodimentsmay be made as is appropriate.

Firstly, FIGS. 1 through 17 show first through fourth embodiments of thepresent invention that relate to a radius end mill in which a main gashface having an end cutting edge is formed on an inner peripheral side ofa distal end portion of a wall surface of a chip discharge flute of atool body, and in which sub gash faces are formed via a step portion onan outer peripheral surface of the main gash face, and corner cuttingedges are formed extending from the distal end of the sub gash faces toan outer circumference.

Of these, in the first embodiment of the present invention which isshown in FIGS. 1 through 4, a tool body 11 is formed from a hardmaterial such as cemented carbide having a circular column-shapedexternal configuration that is centered on an axis O. Note that the toolbody 11 is formed so as to have a rotationally symmetric configurationaround the axis O.

A pair of chip discharge flutes 12 are formed on an outer circumferenceof a distal end portion (i.e., the end portion of the left side in FIGS.1 and 2) of the tool body 11 such that, as they move from the distal endtowards the rear end side, they are helically twisted at a constanttwist angle α around the axis O towards the rear in the rotationdirection T of the tool during a cutting operation.

Wall faces 13 of the chip discharge flutes 12 that face in the toolrotation direction T are formed at a cross-section that is orthogonal tothe axis O as concave curved surfaces that are depressed towards therear side of the tool rotation direction T. Peripheral cutting edges 14are formed on side ridge portions on the outer circumferential side ofthe wall faces 13, while end cutting edges 15 are formed on the distalend side of the wall faces 13. Furthermore, corner cutting edges 16having an arc-shaped external configuration that protrude towards theouter circumferential side at the distal end are formed so as to beconnected to the peripheral cutting edges 14 and the end cutting edges15 on corner portions on the outer circumferential side of the distalend of the wall faces 13 where the peripheral cutting edges 14 and endcutting edges 15 intersect.

Here, in the present embodiment, gashes are formed in two stages oninner and outer circumferences of the distal end portion of the wallfaces 13 that face towards the tool rotation direction T of the chipdischarge flutes 12. Of these, a main gash face 17 is formed by thefirst stage gash on an inner circumferential side of the wall face 13,and the end cutting edge 15 is formed on a distal end edge of the maingash face 17.

The main gash faces 17 are formed in a planar shape by cutting out theinner circumferential side of the distal end portion of the wall face 13in a direction that is substantially parallel to the axis O.Accordingly, the angle of inclination of the main gash faces 17 withrespect to the axis O is set to 0°, and is set as smaller than the twistangle α of the chip discharge groves 12. As is shown in FIG. 3, the endcutting edges 15 are formed so as to extend rectilinearly towards theouter circumferential side from the inner circumference of the tool body11 as seen from the distal end in the axial direction O, and areprovided with a rake angle of 0° in the axial direction that is the sameas the aforementioned angle of inclination.

However, in the present embodiment, as seen in plan view facing the maingash faces 17, the end cutting edges 15 are slightly inclined so as toapproach the distal end side as they move towards the outercircumferential side, as shown in FIG. 1, thereby resulting in the endcutting edges 15 being provided with a concave angle.

On the outer circumferential side of the distal end portion of the wallface 13, sub gash faces 18 are formed on an inner side of theaforementioned corner portion by the second stage gash so as to beadjacent to the outer circumferential side of the main gash face 17. Thecorner cutting edges 16 are formed on side ridge portions on the outercircumferential side of the distal ends of the sub gash faces 18.

The sub gash faces 18 are formed in the same manner as the main gashfaces 17 by cutting the outer circumferential side of distal endportions of the wall faces 13 in a planar shape. However, while the maingash faces 17 extend substantially in parallel to the axis O, as isdescribed above, at points of intersection P between the end cuttingedges 15 and the corner cutting edges 16, the sub gash faces 18intersect with the main gash faces 17 and are slanted so as to graduallyextend away towards the rear side of the tool rotation direction T withrespect to the main gash faces 17 as they approach the rear end side inthe direction of the axis O. Accordingly, an angle of inclination β ofeach sub gash face 18 with respect to the axis O is made larger on thepositive angle side than the angle of inclination with respect to theaxis O of the main gash faces 17 which is 0°.

Moreover, by forming the sub gash faces 18 such that they extend awayfrom the main gash faces 17, the sub gash faces 18 are made adjacent tothe main gash faces 17 via a step portion 19. In the present embodiment,at a cross-section that is orthogonal to the axis O, as shown in FIG. 4,these step portions 19 are formed as planar wall surfaces that areperpendicular to the main gash faces 17. In addition, they are alsoperpendicular to the sub gash faces 18. Furthermore, as shown in FIG. 1,at the aforementioned point of intersection P, the step portions 19 aremade to intersect with the end cutting edges 15 and corner cutting edges16, so that they extend substantially perpendicularly with respect tothe end cutting edges 15 that have been provided with the aforementionedconcave angle.

Moreover, the angle of inclination β of the sub gash faces 18 withrespect to the axis O is made smaller than the twist angle α of the chipdischarge flutes 12 with respect to the axis O. Accordingly, as shown inFIG. 1, at rear ends of these sub gash faces 18, outer circumferentialends of an intersection edge line L where the main gash faces 17intersect with the wall faces 13 are made to intersect with the wallfaces 13 at the point where they pass the rear end side, and an outercircumferential end of an intersection edge line M thereof is taken asan intersection point Q between the peripheral cutting edges 14 and thecorner cutting edges 16. However, if the sub gash face 18 is small, thistype of structure does not need to be employed.

Note that because the wall faces 13 are formed as the above describedconcave curved surfaces, in the above described plan view, theintersection edge lines L and M are formed as convex curved lines thatprotrude towards the distal end side, as shown in FIG. 1.

Moreover, while the corner cutting edges 16 make smooth contact at theintersection points P with the end cutting edges 15 that are formed asstraight lines, as they approach the outer circumferential side at therear end along the protruding arcs formed by the corner cutting edges 16from the intersection points P, they are inclined so as to approach therear end side of the rotation direction T to match the angle ofinclination β of the sub gash faces 18, and intersect with theperipheral cutting edges 14 at the intersection point Q.

Accordingly, in a radius end mill that is constructed in this manner,firstly, the main gash faces 17, which form an angle of inclination thatis smaller (i.e., 0°) with respect to the axis O than the twist angle αof the chip discharge flutes 12, are formed on an inner circumferentialside of the distal end portion of the wall faces 13 that face in thetool rotation direction T of the chip discharge flutes 12, and the endcutting edges 15 are subsequently formed on the distal ends of thesemain gash faces 17. Accordingly, compared with when the wall faces 13are simply extended as they are towards the distal end side so as toform end cutting edges, the included angle of the end cutting edges 15may be increased. As a result, in the end cutting edges 15 in which, onthe inner circumferential side of the tool body 11, the cutting speed isslow and a considerable cutting load is applied, a sufficient edge tipstrength may be secured, and it is possible to lengthen the lifespan ofthe tool by preventing chipping or defects from occurring in the cuttingedge.

On the other hand, because the sub gash faces 18, which are inclinedtowards the rear in the tool rotation direction T as they approach therear end side at the angle of inclination β with respect to the axis Othat is larger than that of the main gash faces 17, are formed in adistal end portion of the wall faces 13 on the outer circumferentialside of the main gash faces 17, and because the substantially protrudingarc-shaped corner cutting edges 16 that are continuous with the outercircumferential sides of the end cutting edges 15 are formed on sideridge portions of the outer circumferential sides of the distal ends ofthe sub gash faces 18, the corner cutting edges 16 may be provided withexcellent sharpness, and a decrease in cutting resistance may beachieved. Accordingly, in particular, in a cutting operation to cut aslanted surface or curved surface of a mold in which the corner cuttingedges 16 are frequently used, an improvement in the cutting efficiencymay be achieved.

Moreover, in the present embodiment, although the angle of inclination βof the sub gash faces 18 is greater than that of the main gash faces 17,it is smaller than the twist angle α of the chip discharge flutes 12.Accordingly, compared with when the corner cutting edges are formed bysimply extending the wall faces 13 as they are as far as the distal endof the tool body 11, a larger included angle may be secured in thecorner cutting edges 16, and it is possible to prevent chipping ordefects occurring in the corner cutting edges 16.

Moreover, as a result of the sub gash faces 18, whose angle ofinclination β with respect to the axis O is different from that of themain gash faces 17, being formed at distal end portions of the wallfaces 13 by making the end cutting edges 15 and corner cutting edges 16,which are formed at the distal end sides of the gash faces, smoothlycontinuous at the intersection points P, the sub gash faces 18 are madeto extend away from the main gash faces 17, and the above described stepportions 19, which are shaped as vertical wall surfaces standing uprightfrom the sub gash faces 18, are formed between the sub gash faces 18 andthe main gash faces 17. In addition, because the step portions 19 areformed so as to extend substantially perpendicularly from theintersection points P to the end cutting edges 15, namely, so as facethe outer circumferential side of the tool body 11, chips that areproduced in portions extending, in particular, from corner portionprotruding ends to the outer circumferential sides of the corner cuttingedges 16 during a cutting operation to cut an inclined surface or curvedsurface of a die or the like, may be made to slide along the top of thesub gash faces 18 and collide with the step portions 19.

As a result, even if the chips are discharged in elongated form, becausethey are subjected to resistance by when they collide against the stepportions 19 and undergo processing such as being curled or broken,according to a radius end mill having the above described structure, animprovement in the processing ability of these chips may also beachieved, and together with a reduction in the cutting resistance of thecorner cutting edges 16, it becomes possible to achieve a smoother diecutting operation and the like.

Note that, in the above described first embodiment, in a cross-sectionwhere the step portions 19 intersect the axis O, they are perpendicularto the main gash faces 17 and are also perpendicular to the sub gashfaces 18. Accordingly, it is possible to provide greater resistance tothe chips that have collided with the step portions 19 and a reliableprocessing thereof may be achieved. However, on the other hand, if theangle of the step portions 19, which form upright wall shapes in themanner described above, with respect to the sub gash faces 18 is a steepgradient, then, depending on the cutting conditions and the like, thechips that have been discharged onto the sub gash faces 18 in the mannerdescribed above may not only be subjected to resistance when theycollide against the step portions 19, but the discharge itself may beobstructed and blockages produced. This may cause an interruption of asmooth chip discharge and, conversely, there is a possibility that thechip processing capability will be deteriorated.

Therefore, in cases such as this, as in the radius end mill of a secondembodiment of the present invention shown in FIGS. 5 through 8, it isdesirable that step portions 20 be formed as inclined surfaces thatgradually extend away as they approach the sub gash face 18 side fromthe main gash face 17 side. Note that, in the second embodiment shown inFIGS. 5 through 8, portions that are the same as in the first embodimentshown in FIGS. 1 through 4 are given the same reference symbols and adescription thereof is omitted.

Here, in the same manner as the step portions 19 of the firstembodiment, as shown in FIG. 5, the step portions 20 of the secondembodiment are formed so as to extend from the intersection point Pbetween the end cutting edges 15 and the corner cutting edges 16 in asubstantially perpendicular direction with respect to the end cuttingedges 15. However, unlike in the first embodiment in which the stepportions 19 are also perpendicular to the main gash faces 17 and subgash faces 18, as shown in FIG. 8, at a cross section where theyintersect with the axis O, the step portions 20 are formed as planarinclined faces that extend away from the main gash faces 17 at aconstant angle of inclination as they move from the main gash faces 17towards the sub gash faces 18. Moreover, in the present embodiment, asshown in FIG. 8, the angle of inclination of the inclined surfaceproduced by the step portion 20 having the constant angle is set withina range of 30 to 60° as an angle of inclination y with respect to adirection that is perpendicular to the sub gash face 18 at a crosssection that intersects the axis O.

Accordingly, in the radius end mill of the second embodiment that isformed in this manner, because the step portions 20 are formed asinclined faces that gradually extend away as they move from the maingash faces 17 side towards the sub gash face 18 side in the mannerdescribed above, the gradient of the step portions 20 as seen from thesub gash face 18 side is more gentle than that of the step portions 19of the first embodiment. Accordingly, even if chips produced at thecorner cutting edges 16 are discharged along the sub gash faces 18 andcollide with the step portions 20, they are subjected to resistance bythe step portions 20 and while being either curled or broken, are guidedalong the slope of the inclined surface formed by the step portion 20,and may be reliably discharged without causing any blockages.

Moreover, in the present embodiment, the angle of inclination γ of theinclined surfaces formed by the step portions 20 are set within a rangeof 30 to 60° with respect to a direction that is perpendicular to thesub gash face 18. As a result, as is described above, chip blockages maybe reliably prevented and a smooth discharge achieved, while at the sametime sufficient resistance is imparted to the chips and smoothprocessing of the chips, such as the curling or breaking thereof, may beachieved. Here, if the rise of the step portions 20 is a steep gradientso as to approach the vertical resulting in the angle of inclination γbeing reduced so as to be less than 30°, then there is a possibility ofit not being possible to sufficiently prevent chip blockages. If,however, the inclination is flattened so that the angle of inclination γis more than 60°, then the resistance that is imparted to collided chipsis too small, and there is a possibility that reliable processing willnot be obtainable.

In this second embodiment, the step portions 20 are formed as planarinclined surfaces having a constant angle of inclination γ, however, asin a third embodiment which is shown in FIG. 9, it is also possible toform step portions 21 as concave curved surfaces, and to make the angleof inclination of the step portions 21 with respect to a direction thatis perpendicular to the sub gash face 18 gradually smaller as it movesfrom the sub gash face 18 side to the main gash face 17 side. Note thatFIG. 9 is a view corresponding to the cross section taken along the lineZ-Z in FIG. 5 of the second embodiment, and portions that are the sameas those in the second embodiment are given the same reference symbols.

Accordingly, in this third embodiment as well, because the step portions21 are formed as inclined surfaces that are gradually extend away asthey move from the main gash face 17 side to the sub gash face 18 side,the same effects as those of the second embodiment may be obtained. Inaddition, because the inclination as seen from the sub gash face 18 sidebecomes a gradually steeper gradient as it moves towards the main gashface 17 side, while chips that are discharged over the sub gash face 18collide at first against the gentle gradient portion of the step portion21 so that blockages may be reliably prevented, they are then pushed asthey are so as to be guided to the steep gradient portion of the maingash face 17 side and gradually become subject to resistance. As aresult, they are more efficiently curled or broken, and disposed of.Namely, according to the radius end mill of the third embodiment, thisradius end mill is more effective in that it achieves both the excellentchip disposal performance of the first embodiment and the smooth chipdischarge performance of the second embodiment.

Next, FIGS. 10 through 17 show a fourth embodiment when the presentinvention, in which the sub gash faces 18 are formed via the stepportions 19, 20, and 21 on the outer circumferential side of the maingash faces 17 in the manner described above, is applied to a throw awaytype of radius end mill. Note that, in this fourth embodiment as well,component elements that are the same as in the above first through thirdembodiments are given the same reference symbols and the descriptionthereof is abbreviated.

Namely, in the first through third embodiments, the chip dischargeflutes 12, main and sub gash faces 17 and 18, step portions 19, 20, and21, peripheral cutting edges 14, end cutting edges 15, and cornercutting edges 16 are formed directly on the circular cylinder-shapedtool body 11 that is formed from a hard material such as a cementedcarbide. However, in the fourth embodiment, the tool body 11 isconstructed by forming an insert mounting seat 32 at a distal endportion of a circular cylinder-shaped holder 31, and removably mountingan indexable insert 33 on this insert mounting seat 32 using an insertclamp mechanism 34. The above described chip discharge flutes 12, mainand sub gash faces 17 and 18, step portions 19, 20, and 21, peripheralcutting edges 14, end cutting edges 15, and corner cutting edges 16 areformed on the indexable insert 33. Note that the holder 31 is formedfrom a steel material or the like, and the indexable insert 33 is formedfrom a hard material such as cemented carbide.

Here, a distal end portion of the holder 31 is formed in a hemisphericalshape. The insert mounting seat 32 is formed as a concave groove thatextends in one direction that is orthogonal to the axis O by cutting thedistal end portion of the holder 31 along a plane that includes the axisO of the tool body 11 such that it is open on the distal end side. Theinsert mounting seat 32 is formed by a pair of wall surfaces 35 and 36that are parallel with the axis O and are also parallel with each othersuch that they face each other, and an end surface 37 that isperpendicular to the wall surfaces 35 and 36 and is also perpendicularto the axis O while facing the distal end side of the holder 31.

The indexable insert 33 is formed in a substantially quadrangular planarshape that is able to be fitted into the concave groove-shaped insertmounting seat 32. The indexable insert 33 is provided with a pair ofside surfaces 38 and 39 that are parallel to each other and are in tightcontact with the wall surfaces 35 and 36 when the indexable insert 33has been fitted, and with a rear end surface 40 that is perpendicular tothe side surfaces 38 and 39 and is in tight contact with the end surface37. Furthermore, a mounting hole 41 having a circular cross section thatpenetrates the indexable insert 33 substantially in the center thereofperpendicularly to the side surfaces 38 and 39 is formed between theside surfaces 38 and 39.

When the tool body 11 has been formed by fitting the indexable insert 33into the insert mounting seat 32 and fixing it in position using theclamp mechanism 34, chip discharge flutes 12 are formed respectively ina spiral configuration on a pair of circumferential surfaces of theindexable insert 33 that are positioned on an outer periphery of thedistal end portion of the tool body 11. In addition, peripheral cuttingedges 14 are formed at side ridge portions on the outer circumferentialside of the wall surfaces 13 that face the tool rotation direction Tside, the main gash faces 17 are formed on an inner circumferential sideat the distal end, and the end cutting edges 15 are formed at side ridgeportions on the distal end side thereof. The sub gash faces 18 areformed via the step portions 19, 20, or 21 on the outer circumferentialside of the main gash faces 17. Convex arc-shaped corner cutting edges16 are formed on the side ridge portions extending from the distal endof the sub gash faces 18 to the outer periphery thereof.

When an indexable insert 33 that has been fitted into the insertmounting seat 32 is positioned such that a center line X of the mountinghole 41 is orthogonal to the axis O of the tool body 11, and is fixed inplace by the clamp mechanism 34, and when the tool body 11 has beenconstructed in this manner, a symmetrical configuration is formed aroundthe axis O. Moreover, out of the hemispherical distal end portion of theholder 31, that portion that is adjacent to the tool rotation directionT side of the pair of chip discharge flutes 12 of the indexable insert33 is formed as a notched portion 31A by a cylindrical surface whoseradius is greater than the radius of this hemisphere.

Accordingly, in the indexable insert type of radius end mill of thefourth embodiment as well in which the peripheral cutting edges 14, theend cutting edges 15, the corner cutting edges 16, the main gash face17, the sub gash face 18, and the step portions 19, 20, and 21 areformed on the indexable insert 33, it is possible to obtain the sameeffects as in the first through third embodiments in accordance with theform of the step portions 19, 20, and 21.

In the clamp mechanism 34 of the present embodiment, by screwing a clampscrew 42 that is inserted from one side (i.e., the wall surface 36 side)of the distal end portion of the holder 31 that is separated into thewall surface 35 side and the wall surface 36 side with the insertmounting seat 32 in-between and penetrates the indexable insert 33 toreach the other side (i.e., the wall surface 35 side) in order to clampthe indexable insert 33 that has been fitted into the insert mountingseat 32, not only is the distal end portion of the holder 31 elasticallydeformed so as to sandwich the indexable insert 33, but the clamp screw42 itself is also elastically deformed and is bent in a direction thatintersects the screwing-in direction. As a result, the indexable insert33 is pushed in the bending direction and is clamped.

Here, the clamp screw 42 has a male thread portion 42A at one endthereof and has a flat countersunk head portion 42B whose underside isin the form of a cone at the other end thereof. Between the malethreaded portion 42A and the head portion 42B is formed a columnar shaftportion 42C that has an external diameter that enables it to bepress-fitted inside the mounting hole 41, and has an axial length thatis slightly longer than the gap between the wall surfaces 35 and 36 ofthe insert mounting seat 32.

Moreover, in one of the portions of the distal end portion of the holder31, which is separated by the concave groove-shaped insert mounting seat32, that is on the wall surface 35 side (i.e., the aforementionedportion on the other side) of the insert mounting seat 32 is formed ascrew hole 43 that penetrates this portion so as to be perpendicular tothe wall surface 35. The screw hole 43 is formed so as to be coaxialwith the center line X of the indexable insert 33 that has beenpositioned in the manner described above. The portion of this screw hole42 that opens onto the wall surface 35 is formed as a cross-sectionallycircular hole 43A that has the same internal diameter as the mountinghole 41 of the indexable insert 33, and is formed such that the endportion on the male threaded portion 42A side of the shaft portion 42Cof the clamp screw 42 is able to be press-inserted therein. A femalethreaded portion 43B into which the male threaded portion 42A of theclamp screw 42 is threaded is formed in the portion on the opposite sidefrom the wall portion 35 that is beyond the circular hole 43A.

In that portion of the distal end portion of the holder 31 that is onthe wall surface 36 side (i.e., the aforementioned portion on the oneside) of the insert mounting seat 32 as well is formed a through hole44, into which the clamp screw 42 is inserted, perpendicularly to thewall surface 36 so as to penetrate that portion. This through hole 44 isan elongated hole that is formed such that, at any position in thecenter line X direction of the indexable insert 33 that has beenpositioned in the manner described above, a cross-section thereof thatis parallel to the wall surface 36 is in the shape of an elongated holehaving a major axis that extends in a direction that is parallel to theaxis O, as shown in FIG. 17, namely, in a direction that intersects thecenter line X direction in which the clamp screw 42 is threaded.Moreover, the center of that half arc portion of the circumference ofthe ellipse that is on the distal end side (i.e., the left side in FIG.17) of the tool body 11 is positioned on the center line X, and thisdistal end side half arc portion and the rear end side half arc portionare connected together by a pair of tangent lines at both ends of thesehalf arcs that are in parallel with the major axis and also in parallelwith each other.

Furthermore, the portion of the through hole 44 that opens onto the wallsurface 36 is set to the same size as the inner diameter (i.e., thediameter) of the half arc of the ellipse formed by the aforementionedcross section, and the gap between the pair of tangent lines, namely,the width W of the ellipse is set to the same size as the inner diameter(i.e., the diameter) E of the circular hole 43A of the screw hole 43 ofthe wall surface 35 on the opposite side and as the inner diameter(i.e., the diameter) of the mounting hole 41 in the indexable insert 33,and the shaft portion 42C of the clamp screw 42 is formed as an engagingportion 44A that has a width that enables it to be press-insertedbetween at least the pair of tangent line portions. Moreover, theportion on the opposite side from the wall surface 36 that is beyondthis engaging portion 44A forms an inclined portion 44B that is inclinedsuch that a radius of a half arc of the ellipse formed by the crosssection thereof and the interval between the pair of tangent linesbecome gradually larger as they move towards the opposite side from thewall surface 36. The angle of inclination of this inclined portion 44Bis equal to the taper angle of the conical surface formed by theunderside of the head portion 42B of the clamp screw 42.

Note that, in an aperture portion 44C that opens onto an outer peripheryof the distal end portion of the holder 31 on the opposite side from thewall surface 36 beyond the inclined portion 44B, the inner diameter(i.e., the diameter) of a half arc of the ellipse formed by the crosssection of the insertion hole 44 and the interval between the tangentlines is set at a uniform size that is larger than the diameter of thehead portion 42B. Moreover, in order to make the distal end portion ofthe holder 31 easily elastically deformable, a narrow slit 45 that formsa hollow sinking from the end surface 37 towards the rear end side ofthe tool body 11 is formed extending in parallel with the wall surface36 on the wall surface 36 side of the end surface 37 of the insertmounting seat 32.

In this type of clamp mechanism 34, by inserting the indexable insert 33into the insert mounting seat 32 such that, as is described above, thecenter line X of the mounting hole 41 is orthogonal to the axis O, themounting hole 41 and the circular hole 43A of the screw hole 43 thatboth have the same inner diameter (i.e., diameter) E, as well as thehalf arc portion of the cross section of the distal end side of the toolbody 11 of the engaging portion 44A of the insertion hole 44 are bothpositioned above the inner surface of the same cylinder that has itscenter on the center line X. Therefore, if the clamp screw 42 that hasbeen inserted from the aperture portion 44C side of the insertion hole44 is inserted through the mounting hole 41, and the male threadedportion 42A thereof is screwed into the female threaded portion 43B ofthe screw hole 43, the columnar shaft portion 42C of the clamp screw 42is fitted so as to be in tight contact with the inner surface of thecylinder, and the indexable insert 33 is placed in position.

In addition, if the clamp screw 42 is screwed in further, the conicalsurface of the underside of the head portion 42B presses the portionhaving a half arc cross section at the distal end side of the tool body11 of the inclined portion 44B of the insertion hole 44. As a result,the distal end portion of the holder 31 on the wall surface 36 sidewhere the insertion hole 44 is formed is slightly elastically deformedtowards the wall surface 35 side, so that the side surfaces 38 and 39are pressed by the two wall surface 35 and 36. As a result, theindexable insert 33 is sandwiched in the insert mounting seat 32 andfixed in position.

At the same time as this, in the clamp screw 42, a portion extendingfrom the head portion 42B to the shaft portion 42C is slightlyelastically deformed by a reaction force against the force with whichthe conical surface of the underside of the head portion 42B pressesagainst the distal end side of the inclined portion 44B of the insertionhole 44 so as to bend towards the rear end side of the tool body 11along the major axis of the ellipse formed by the cross section of theinsertion hole 44. In addition, because, in conjunction with this, theinner circumferential surface of the mounting hole 41 into which theshaft portion 42C has been inserted is also pushed in the direction inwhich the clamp screw 42 is bent, the indexable insert 33 is alsosubjected to pressing force towards the rear end side of the tool body11 such that the rear end surface 40 of the indexable insert 33 ispushed against the end surface 37 of the insert mounting seat 32,thereby more firmly fixing the indexable insert 33 in position. Notethat the end portion on the male threaded portion 42A side of the shaftportion 42C that has been inserted into the circular hole 43A of thescrew hole 43 is not deformed, and the clamp screw 42 is bent such thatthe head portion 42B is tilted to the rear end side pivoting on thecenter of this portion.

If a case is hypothesized in which the ability to throw away the radiusend mill as is described, for example, in Japanese Patent Application,Firs Publication No. S59-175915 has been achieved, and, in the samemanner as in the present embodiment, a cutting edge is formed in anindexable insert that is fitted into a concave groove-shaped insertmounting seat that is formed in a holder, and the holder distal endportion and the clamp screw are elastically deformed by a clampmechanism that is provided with a clamp screw that is inserted into amounting hole in this indexable insert, thereby fixing the indexableinsert in position, then this indexable insert is fixed in position inthe axial direction of the tool body by being pressed against the insertmounting seat end surface by the bending of the clamp screw. Moreover,the indexable insert is also fixed in position in the direction of thecenter line of the mounting hole in the indexable insert, which isorthogonal to the above axial direction, by the two wall surfaces of theinsert mounting seat sandwiching and also pressing the indexable insert.

However, in a direction that is orthogonal to both the axis of the toolbody and the direction of the center line in the mounting hole, namely,in the direction in which the concave groove-shaped insert mounting seatthat is formed in the distal end portion of the holder extends, theindexable insert is only supported by the shaft portion of the clampscrew that is inserted into the mounting hole in the indexable insert.Conversely, in order to make this shaft portion of the clamp screwelastically deformable, the insertion hole in the distal end portion ofthe holder into which the portion of the shaft portion that iselastically deformed is inserted must be made larger than the outerdiameter of this shaft portion. Therefore, for example, if the insertionhole in the distal end portion of the holder is simply made larger thanthe outer diameter of the shaft portion, then when the indexable insertis positioned and then fixed in position by screwing in the clamp screw,or when a load is applied during a cutting operation, the clamp screw isalso bent in the direction in which the insert mounting seat extends sothat there is a possibility of the indexable insert working loose andthe work accuracy deteriorating markedly.

Therefore, in the present embodiment, as is described above, by formingthe insertion hole 44 on the wall surface 36 side of the distal endportion of the holder 31 into which the clamp screw 42 is inserted suchthat it has an elliptical cross section, and by forming the engagingportion 44A in the insertion hole 44 such that it has a width W thatallows the shaft portion 42C of the clamp screw 42 to be fitted insideit, while bending in the direction of the axis O due to elasticdeformation of the clamp screw 42 is still allowed, bending of the clampscrew 42 in the direction in which the insert mounting seat 32 extends,which is perpendicular to both the axis O direction and the center lineX direction (i.e., the direction in which the clamp screw 42 is screwedin), is restricted as a result of the shaft portion 42C being engagedwith the engaging portion 44A in this direction.

Namely, in the present embodiment, in order to prevent any deteriorationin the processing accuracy that is caused by slipping of the indexableinsert 33 as is described above, by screwing in the clamp screw 42 thatis inserted from the one side of the distal end portion of the holder31, which has the insert mounting seat 32 sandwiched between it, andpenetrates the indexable insert 33 such that the clamp screw 42 isscrewed in as far as the other side of the distal end portion of theholder 31, the clamp mechanism 34 of the indexable insert 33 sandwichesthe indexable insert 33, which has been fitted into the concavegroove-shaped insert mounting seat 32 that is formed in the distal endportion of the holder 31, between both sides of the distal end portionof the holder 31, and clamps the indexable insert 33 by pushing it inthe bending direction of the clamp screw 42 by bending the clamp screw42 in a direction that intersects the direction in which the clamp screw42 is screwed in. This clamp mechanism 34 for an indexable insert 33 isalso characterized in that an engaging portion 44A having the shape ofan elongated hole that, in a state in which the clamp screw 42 isscrewed in to the other side of the distal end portion of the holder 31,has a width W that enables the shaft portion 42C of the clamp screw 42to be inserted therein and that extends in the bending direction isformed in the insertion hole 44 that is formed in one side of the distalend portion of the holder 31 and into which is inserted the clamp screw42.

Accordingly, as a result of the shaft portion 42C engaging with thisengaging portion 44A, the clamp screw 42 is no longer bent in anydirection other than the bending direction out of all the directionsthat intersect the screwing in direction of the clamp screw 42, and itis possible to prevent the indexable insert 33 from slipping while theclamp screw 42 is being screwed in or during a cutting operation. As aresult, a cutting operation may be performed while the indexable insert33 is being held with accuracy symmetrically around the axis O of thetool body 11, thereby enabling a high degree of processing accuracy tobe obtained.

Moreover, in the present embodiment, a circular hole 43A into which theend portion of the shaft portion 42C is able to be inserted is formed inthe screw hole 43 that is formed on the other side of the distal endportion of the holder 31 and into which the clamp screw 42 is screwed.Accordingly, there is no load from bending on the male threaded portion42A of the clamp screw 42 that is formed on this end portion side, andit is possible to bend the shaft portion 42C around this end portion,and damage to the clamp screw 42 may be prevented. In addition, becausethe inner diameter (i.e., the diameter) E of the circular hole 43A andthe width W of the engaging portion 44A are made equal, and because theshaft portion 42C of the clamp screw 42 that is fitted into the circularhole 43A and the engaging portion 44A is also formed as a circularcolumn having a fixed outer diameter, load caused by bending is reducedin this shaft portion 42C as well, and the shaft portion 42C may beuniformly bent so that damage thereto may be prevented.

Furthermore, a cross section of the engaging portion 44A is formed as anelongated hole, and the side of the engaging portion 44A that is on thedistal end side of the tool body 11, namely, the opposite side from thebending direction is formed as a half arc of the inner diameter (i.e.,the diameter) E that is equal to the circular hole 43A, and, as isdescribed above, is positioned on the same cylindrical surface as thecircular hole 43A. As a result, when the circular hole 43A and theengaging portion 44A are being formed, firstly, a hole is made in thecylindrical surface portion of the inner diameter E using a drill or thelike, so as to form the half arc portions of the circular hole 43A andthe engaging portion 44A. Next, a cutting operation is performed usingan end mill or the like at the inner diameter (i.e., the diameter) E ofthe cylindrical surface, namely, at the width W of the engaging portion44A such that the engaging portion 44A is widened in the above describedbending direction. The advantage may also be obtained that theprocessing to form the circular hole 43A and the engaging portion 44Aaccurately is simple.

Note that the clamp mechanism 34 itself of the above described type ofindexable insert 33 may also be applied, in addition to the indexabletype of radius end mill of the present embodiment, to indexable types ofball end mill and square end mill, or to various indexable types ofcutting tool in addition to these.

Next, FIGS. 18 through 30 show a fifth through eighth embodiments of thepresent invention that relate to a radius end mill in which an inneredge of a rake face of an end cutting edge and an inner edge of a rakeface of a corner cutting edge are formed as a smoothly continuous singleconvex curve.

As is shown in FIGS. 18 through 21, the radius end mill according to thefifth embodiment has a substantially columnar shaped tool body 50 thatis formed from a hard material such as a cemented carbide and is rotatedaround an axis O. Note that the tool body 50 as well is formed so as tohave a rotationally symmetric configuration around the axis O.

For example, two chip discharge flutes 51 are formed substantiallyequidistantly in the circumferential direction on an outer circumferenceof the tool body 50 so as to be open to the outer circumferentialsurface of the tool body 50. The two chip discharge flutes 51 are formedsuch that, as they move towards the rear end side in the direction ofthe axis O, they are helically twisted at a predetermined twist angle θaround the axis O towards the rear in the tool rotation direction T.

For example, two gashes 52 are formed equidistantly in thecircumferential direction at a distal end of the tool body 50 so as tobe open to the distal end surface of the tool body 50 and so as toseparate this distal end surface into a plurality of segments. In thesame manner as the chip discharge flutes 51, the two gashes 52 areformed such that, as they move towards the rear end side in thedirection of the axis O, they are twisted towards the rear in the toolrotation direction T.

The rear end portions of the gashes 52 are made continuous with thedistal end portions of the chip discharge flutes 51, and the gashes 52and chip discharge flutes 51 are in a state of communicating with eachother.

Moreover, wall surfaces that face towards the front side in the toolrotation direction T of the chip discharge flutes 51 that are formed onan outer circumference of the tool body 50 are formed as outercircumferential rake faces 51A. Peripheral cutting edges 54 are formedon ridge line portions that are positioned at an outer circumferentialside of the outer circumferential rake faces 51A, namely, are positionedon intersecting ridge line portions between the outer circumferentialrakes faces 51A and outer circumferential flank faces 53 that intersectwith the outer circumferential rake faces 51A and face towards the outercircumferential side of the tool body.

Here, because the rear end portions of the gashes 52, which are formedat the distal end of the tool body 50, are formed so as to be continuouswith the distal end portions of the chip discharge flutes 51, rear endportions in the direction of the axis O of the wall surfaces of thegashes 52 that face towards the front in the tool rotation direction Textend as far as the distal end portions of the outer circumferentialrake faces 51A, which are wall surfaces that face forwards in the toolrotation direction T of the chip discharge flutes 51, and the two arecontinuous with each other.

As a result, with rear end portions in the direction of the axis O ofthe wall surfaces that face forwards in the tool rotation direction T ofthe gashes 52 forming outer circumferential distal end portion rakefaces 52C, portions on the distal end side of the peripheral cuttingedges 54 (i.e., peripheral cutting edge distal end portions 54A) areformed in outer circumferential ridge line portions of these outercircumferential distal end portion rake faces 52C, namely, inintersection ridge line portions where the outer circumferential distalend portion rake faces 52C intersect with the outer circumferentialflank faces 53 that face the outer circumferential side of the tool body50.

Moreover, portions on the inner circumferential side of the tool body 50of the distal end portions in the direction of the axis O of the wallsurfaces that face forwards in the tool rotation direction T of thegashes 52 form distal end rake faces 52A, while portions on the outercircumferential side of the tool body 50 of the distal end portions inthe direction of the axis O of the wall surfaces that face forwards inthe tool rotation direction T of the gashes 52 form corner rake faces52B.

In addition, end cutting edges 56 that extend to the outercircumferential side of the tool body 50 from the vicinity of the axis Oare formed on ridge line portions that are positioned on the distal endside of the distal end rake faces 52A, namely, are positioned onintersecting ridge line portions between the distal end rake faces 52Aand distal end flank faces 55 that intersect with the distal end rakefaces 52A and face towards the distal nd side in the direction of theaxis O. Note that the end cutting edges 56 are slightly slanted so as toapproach the distal end side in the direction of the axis O as they movetowards the outer circumferential side of the tool body 50 from thevicinity of the axis O.

Furthermore, substantially quarter arc-shaped corner cutting edges 58are formed on ridge line portions that are positioned on the outercircumferential side of the distal end of the corner rake faces 52B,namely, are positioned on intersecting ridge line portions between thecorner rake faces 52B and corner flank faces 57 that intersect with thecorner rake faces 52B and face towards the outer circumferential side ofthe tool body 50 and towards the distal end side in the direction of theaxis O.

Note that a radius of curvature “r” of the substantially arc-shapedportions formed by the corner cutting edges 58 is set such that a ratior/D between the radius of curvature “r” and a diameter D of the toolbody 50 (i.e., the diameter of a circle S1 that touches the exterior ofa cross section that is orthogonal to the axis O of the tool body 50:see FIG. 21) is 0.2 or more, while “r” is also set such that a ratiobetween “r” and the diameter D and web thickness “d” (i.e., the diameterof a circle S2 that touches the interior of a cross section that isorthogonal to the axis O of the tool body 50: see FIG. 21) is (D−d)/2 ormore.

The end cutting edges 56 are smoothly continuous with the peripheralcutting edges 54 via the substantially quarter arc-shaped corner cuttingedges 58. Namely, the substantially quarter arc-shaped corner cuttingedges 58 constitute an intersecting portion (i.e., a corner portion)where the end cutting edges 56 and the peripheral cutting edges 54 eachintersect, and the radius end mill of this fifth embodiment is atwo-edge radius end mill that has two cutting edges that are smoothlycontinuous from the end cutting edges 56 to the peripheral cutting edges54 via the corner cutting edge 58.

In each of these two cutting edges, when seen from the distal end sidein the direction of the axis O, the end cutting edges 56 and cornercutting edges 58 present a gentle convex curve that protrudes forwardsin the tool rotation direction T, while because the chip dischargeflutes 51 and the gashes 52 are formed in a twisted shape as isdescribed above, the corner cutting edges 58 and peripheral cuttingedges 54 are formed so as to twist towards the rear in the tool rotationdirection T as they move towards the rear end side in the direction ofthe axis O.

In addition, in the present embodiment, if the tool body 50 is viewedfrom a direction that is orthogonal to the axis O and that faces thewall surfaces (i.e., the distal end gash face 52A, the corner gash face52B, and the outer circumferential distal end portion rake face 52C) ofthe gash 52 that face forwards in the tool rotation direction T, asshown in FIG. 18, the inner edge 59A of the distal end rake face 52A(i.e., the boundary edge between the distal end rake face 52A and a wallsurface 52D of the gash 52 that stands out on the forward side in thetool rotation direction T of the distal end rake face 52A), the inneredge 59B of the corner rake face 52B (i.e., the boundary edge betweenthe corner rake face 52B and a wall surface 52D of the gash 52 thatstands out on the forward side in the tool rotation direction T of thecorner rake face 52B), and the inner edge 59C of the outercircumferential distal end portion rake face 52C (i.e., the boundaryedge between the outer circumferential distal end portion rake face 52Cand a wall surface of the chip discharge flutes 51 that stands out onthe forward side in the tool rotation direction T of the outercircumferential distal end portion rake face 52C) are smoothlycontinuous with each other, so that altogether they form a single convexcurve that protrudes towards the corner cutting edge 58 side. However,the radius of curvature of the convex curve formed by the inner edges59A, 59B, and 59C is greater than the radius of curvature “r” of thesubstantially arc shape formed by the corner cutting edge 58.

In conjunction with this, the distal end rake face 52A, the corner rakeface 52B, and the outer circumferential distal end portion rake face52C, which are wall surfaces that face forwards in the tool rotationdirection T of the gashes 52 are also formed as a smoothly continuoussingle curved surface.

Note that, for the rake angle in the axial direction (i.e., the angleformed by the direction of the axis O and the rake face, with a positiveinclination that moves towards the rearward side in the tool rotationdirection T as it moves towards the rear end side in the direction ofthe axis O) of the rake face (i.e., the distal end rake face 52A, thecorner rake face 52B, and the outer circumferential distal end portionrake face 52C) that is formed by this single curved surface, the axialdirection rake angle δ in the vicinity of the end cutting edges 56 isset within a range of 0°≦δ≦20°, and the axial direction rake angle ε inthe vicinity of the peripheral cutting edge distal end portions 54A isset so as to satisfy the range of δ≦εand 0°≦(θ−ε)≦10° due to itsrelationship with the axial direction rake angle δ in the vicinity ofthe end cutting edges 56 and the twist angle θ of the chip dischargeflutes 51.

According to the radius end mill of the fifth embodiment constructed inthe above described manner, because the inner edge 59A of the distal endrake face 52A, the inner edge 59B of the corner rake face 52B, and theinner edge 59C of the outer circumferential distal end portion rake face52C are formed as a single smoothly continuous convex curve, unlike theconventional structure, there is no corner portion formed by the inneredges of the rake faces intersecting each other on these rakes faces(i.e., on the distal end rake face 52A, the corner rake face 52B, andthe outer circumferential distal end portion rake face 52C).

As a result, it is possible to increase the spacings between the endcutting edges 56, the corner cutting edges 58, and the peripheralcutting edge distal end portions 54A and the inner edges 59A, 59B, and59C of the rake faces thereof by the amount obtained by obviating thesecorner portions. Namely, by securing a sufficiently large space for thegashes 52 that are formed in the tool body 50, and by sufficientlyenlarging the space for discharging chips, it is possible to maintain anexcellent chip discharge performance when cutting a work piece.

In the same manner, as a result of the inner edges 59A, 59B, and 59C ofthe rake faces (i.e., of the distal end rake face 52A, the corner rakeface 52B, and the outer circumferential distal end portion rake face52C) being formed as a single continuous convex curve, when chips thatare generated by the cutting of a work piece are discharged, there is noplace (i.e., corner portion) where these chips may become caught, andthe chips may be discharged smoothly. Because of this as well, it ispossible to maintain an excellent chip discharge performance.

In addition, in this fifth embodiment, because the distal end rake face52A, the corner rake face 52B, and the outer circumferential distal endportion rake face 52C are smoothly continuous with each other so as toform a single curved surface without any differences in level, chipsgenerated by the cutting of a work piece may be made to pass smoothlyover the rakes faces 52A, 52B, and 52C, resulting in a furtherimprovement in the chip discharge performance being made possible.

Moreover, if these rake faces 52A, 52B, and 52C are formed as acontinuous curved surface with no differences in level, it is alsopossible to achieve an improvement in the operating accuracy of thecorner portions and a reduction in manufacturing time.

Here, while in the radius end mill of this fifth embodiment, because theratio r/D between the radius of curvature “r” of the substantiallyarc-shaped portions formed by the corner cutting edges 58 and a diameterD of the tool body 50 is set to 0.2 or more, and the radius of curvature“r” of the corner cutting edges 58 is (D−d)/2 or more with respect tothe diameter D and web thickness “d” of the tool body 50, and becausethe substantially arc-shaped corner cutting edges 58 are formedcomparatively larger, conventionally, there was a tendency for thespacings between the corner cutting edges 58, end cutting edges 56, andperipheral cutting edge distal end portions 54A and the inner edges 59A,59B, and 59C of the rakes faces thereof to be too large, and it has notbeen possible to form gashes 52 having a sufficient size so that thechip discharge performance was deteriorated. In contrast to this, theproblem of the chip discharge performance may be solved by the effectthat is obtained due to the fact that the inner edges 59A, 59B, and 59Cform a single continuous convex curve, and by the effect that isobtained due to the fact that the rake faces 52A, 52B, and 52C form asingle continuous curved surface.

In this manner, the present invention in which the inner edge 59A of therake face 52A of the end cutting edge 56 and the inner edge 59B of therake face 52B of the corner cutting edge 58 are formed as a smoothlycontinuous convex curve exhibits a greater effect in cases such as whenthe ratio r/D between the radius of curvature “r” of the substantiallyarc-shaped portion formed by the corner cutting edges 58 and thediameter D of the tool body 50 is set to 0.2 or more, and in cases suchas when the radius of curvature “r” of the substantially arc-shapedportions formed by the corner cutting edges 58 is set to (D−d)/2 or morefor the diameter D and web thickness “d” of the tool body 50. However,if a particularly conspicuous effect is anticipated, the presentinvention may also be applied to a radius end mill in which the ratior/D is set to 0.3 or more or in which the radius of curvature “r” is setto (D−d)/2 or more.

Cases such as these (i.e., when the ratio r/D is 0.3 or more) are nowdescribed as a sixth embodiment of the present invention with referencemade to FIGS. 22 through 24 (portions that are the same as those of theabove fifth embodiment are given the same reference symbols and adescription thereof is omitted).

In the radius end mill according to the sixth embodiment, chip dischargeflutes are not formed on an outer circumference of the tool body 50,while rear end portions of the gashes 52 that are formed at the distalend of the tool body 50 are formed so as to be cut upwards to the outercircumferential surface of the tool body 50.

Moreover, rear end portions in the direction of the axis O of the wallsurfaces of the gashes 52 that face forwards in the tool rotationdirection T form outer circumferential rake faces 52C, while peripheralcutting edges 54 are formed on ridge line portions (i.e., onintersecting ridge line portions between the outer circumferential rakefaces 52C and the outer circumferential flank faces 53) that arepositioned on the outer circumferential side thereof.

Furthermore, portions on the inner circumferential side of the tool body50 of the distal end portions in the direction of the axis O of the wallsurfaces that face forwards in the tool rotation direction T of thegashes 52 form distal end rake faces 52A, and end cutting edges 56 areformed on ridge line portions that are positions on the distal end sidethereof, while portions on the outer circumferential side of the toolbody 50 of the distal end portions in the direction of the axis O of thewall surfaces that face forwards in the tool rotation direction T of thegashes 52 form corner rake faces 52B. Substantially quarter arc-shapedcorner cutting edges 58 are formed on ridge line portions that arepositioned on the outer circumferential side of the distal end of thecorner rake faces 52B.

The substantially quarter arc-shaped corner cutting edges 58 constitutean intersecting portion (i.e., a corner portion) where the end cuttingedges 56 and the peripheral cutting edges 54 each intersect, and in theradius end mill of this sixth embodiment, the ratio r/D between theradius of curvature “r” of the substantially arc-shaped portion formedby the corner cutting edges 58 and the diameter D of the tool body 50 isset to 0.3 or more.

In the radius end mill according to this sixth embodiment as well, byforming the inner edge 59A of the distal end rake face 52A, the inneredge 59B of the corner rake face 52B, and the inner edge 59C of theouter circumferential rake face 52C (i.e., a boundary line between theouter circumferential rake face 52C and the wall surface of the gash 52Dthat protrudes towards the front in the tool rotation direction T fromthe outer circumferential rake face 52C) as a single continuous convexcurve, and by forming the distal end rake face 52A, the corner rake face52B, and the outer circumferential rake face 52C as a single continuouscurved surface, the same effects as those of the above described fifthembodiment may be obtained.

In particular, in the radius end mill according to the sixth embodiment,because the ratio r/D between the radius of curvature “r” of thesubstantially arc-shaped portions formed by the corner cutting edges 58and the diameter D of the tool body 50 is set to 0.3 or more, andbecause the substantially arc-shaped corner cutting edges 58 are formedhaving an extremely large size. In a case such as this, if the internaledges intersect at an obtuse angle and forming a corner portion, as in aconventional radius end mill, it is not possible to avoid the spacingbetween the corner cutting edges 58, end cutting edges 56, andperipheral cutting edges 54 and the inner edges 59A, 59B, and 59C ofthese rake faces from becoming extremely small, and the space for thegashes 52 is decreased so that the chip discharge performancedeteriorates into an extremely poor state. However, in this very type ofsituation, by applying the present invention, it is possible to usefullyexhibit the improved effects in the chip discharge performance that areobtained by the fact that the inner edges 59A, 59B, and 59C form asingle continuous convex curve, and by the fact that the rake faces 52A,52B, and 52C form a continuous curved surface.

Furthermore, FIGS. 25 through 30 show a seventh embodiment in which theradius end mill of the present invention, in which the inner edge 59A ofthe rake face 52A of the end cutting edge 56 and the inner edge 59B ofthe rake face 52B of the corner cutting edge 58 are formed as a singlesmoothly continuous curve, is formed as a indexable type in the samemanner as in the fourth embodiment. Moreover, in the same manner as inthe sixth embodiment, in particular, a case is shown in which the radiusof curvature “r” of the substantially arc-shaped portions formed by thecorner cutting edges 58 and the diameter D of the tool body 50 is set to0.3 or more.

Namely, in the seventh embodiment as well, The tool body 50 isconstructed by forming a concave groove-shaped insert mounting seat 32in a distal end portion of a holder 31 that is shaped as a circularcolumn formed from steel or the like, and then fitting a planarindexable insert 60 that is made from a hard material such as a cementedcarbide into this insert mounting seat 32, and attaching it such that itmay be removed therefrom using the insert clamp mechanism 34.

In addition, the end cutting edges 56 and the substantially arc-shapedcorner cutting edges 58 are formed in the above described indexableinsert 60 of the tool body 50 that is constructed in this manner, andthe inner edge 59A of the rake face 52A of this end cutting edge 56 andthe inner edge 59B of the rake face 52B of the corner cutting edge 58are formed as a single smoothly continuous concave curve, and the rakeface 52A of the end cutting edge 56 and the rake face 52B of the cornercutting edge 58 are formed as a single smoothly continuous curvedsurface.

Note that, in this seventh embodiment, the remaining component elementsthat are the same as in the fifth and sixth embodiments are given thesame reference symbols and a description thereof is omitted. Moreover,component elements of the above indexable insert 60 and clamp mechanism34 that are the same as those of the indexable insert 33 and clampmechanism 34 of the fourth embodiment are also given the same referencesymbols and the description thereof is simplified. In particular, thedrawings shown in FIGS. 16 and 17 are also used for the clamp mechanism34 and a drawing thereof is omitted.

Furthermore, the seventh embodiment employs the same structure as thatof the fifth embodiment for the peripheral cutting edges 54, namely, therake faces (i.e., the outer circumferential distal end portion rakefaces) 52C of the peripheral cutting edges 54A that are formed insidethe gashes 52 on the distal end side of the peripheral cutting edges 54form a single curved surface that is smoothly continuous with the rakefaces 52A and 52B of the end cutting edges 56 and the corner cuttingedges 58. Furthermore, the inner edges 59C of the outer circumferentialdistal end portion rake faces 52C form a single convex curve that issmoothly continuous with the inner edges 59A and 59B of the rake faces52A and 52B.

Moreover, when the tool body 50 has been constructed, the indexableinsert 60 is also formed so as to have a rotationally symmetricconfiguration around the axis O, and the outer diameter D of the toolbody 50 in the present embodiment is a circular diameter that, when thetool body 50 has been constructed, is in contact with the exterior of across section of the distal end portion of the tool body 50 that isorthogonal to the axis O. In addition, the outer diameter D is themaximum diameter of the rotation trajectory around the axis O of thecorner cutting edge 58 and the peripheral cutting edge 54 on the outercircumferential side of the indexable insert 60.

Accordingly, in the radius end mill according to this seventh embodimentas well, the same effects as those of the above described fifth andsixth embodiments may be obtained.

Moreover, in order to prevent any deterioration in the processingaccuracy that is caused by slipping of the indexable insert 60 in thesame manner as in the above described fourth embodiment, by screwing inthe clamp screw 42 that is inserted from the one side of the distal endportion of the holder 31, which has the insert mounting seat 32sandwiched between it, and penetrates the indexable insert 60 such thatthe clamp screw 42 is screwed in as far as the other side of the distalend portion of the holder 31, the clamp mechanism 34 of the indexableinsert 60 of the seventh embodiment as well sandwiches the indexableinsert 60, which has been fitted into the concave groove-shaped insertmounting seat 32 that is formed in the distal end portion of the holder31, between both sides of the distal end portion of the holder 31, andclamps the indexable insert 60 by pushing it in the bending direction ofthe clamp screw 42 by bending the clamp screw 42 in a direction thatintersects the direction in which the clamp screw 42 is screwed in. Thisclamp mechanism 34 for an indexable insert 60 is also characterized inthat an engaging portion 44A having the shape of an elongated hole that,in a state in which the clamp screw 42 is screwed in to the other sideof the distal end portion of the holder 31, has a width that enables theshaft portion 42C of the clamp screw 42 to be inserted therein and thatextends in the bending direction is formed in the insertion hole 44 thatis formed in one side of the distal end portion of the holder 31 andinto which is inserted the clamp screw 42.

Furthermore, the fact that the circular hole 43A, into which the endportion of the shaft portion 42C is able to be inserted, is formed inthe threaded hole 43 that is formed on the other side of the distal endportion of the holder 31 and into which the clamp screw 42 is screwed,the fact that the inner diameter (i.e., the diameter) E of the circularhole 43A and the width W of the engaging portion 44A are made equal aswell as the fact that the shaft portion 42C of the clamp screw 42 thatis fitted inside both the circular hole 43A with the engaging portion44A is formed as a circular column having a constant outer diameter, andthe fact that the engaging portion 44A is formed having an ellipticalcross section and the opposite side thereof from the bending directionis formed as a half arc of the inner diameter (i.e., the diameter) Ethat is equal to the circular hole 43A, and is positioned on the samecylindrical surface as the circular hole 43A are all the same as in theclamp mechanism 34 of the fourth embodiment.

Accordingly, in the seventh embodiment as well, in the same manner as inthe above described fourth embodiment, it is possible to prevent theindexable insert 60 from slipping while the clamp screw 42 is beingscrewed in or during a cutting operation, thereby enabling a high degreeof processing accuracy to be obtained. Moreover, the effects areobtained that damage to the clamp screw 42 is prevented, and thecircular hole 43A and engaging portion 44A may be formed accurately andeasily.

Moreover, in the same manner as in the fourth embodiment, the clampmechanism 34 itself of the above described indexable insert 60 may alsobe used, in addition to a radius end mill, in various indexable types ofcutting tool including ball end mills and square end mills.

Furthermore, as is described above, the present invention is not limitedto each of the above described first through seventh embodiments, andvarious combinations of the respective component elements of theseembodiments may be made as is appropriate.

For example, in the first through fourth embodiments, the inner edges ofthe main gash faces 17 that correspond to the rake faces 52A of the endcutting edges 56 of the fifth through seventh embodiments, and the inneredges that are positioned on the inner side via the step portions 19,20, and 21 from the sub gash faces 18 that correspond to the rake faces52B of the corner cutting edges 58, or, in addition to these, the inneredges of the wall surfaces 13 that face the tool rotation direction Tside of the chip discharge flutes 12 that correspond to the rake faces51A (i.e., the outer circumferential distal end portion rake faces 54A)of the peripheral cutting edges 54 (i.e., the peripheral cutting edgedistal end portions 54A) may also be formed as a single smoothlycontinuous convex curve. Alternatively, conversely, instead of the rakesfaces 52A of the end cutting edges 56 and the rake faces 52B of thecorner cutting edges 58 forming single smoothly continuous curvedsurfaces in the fifth through seventh embodiments, it is also possibleto employ a structure in which, the sub gash faces 18 in which the angleof inclination with respect to the axis O is greater than that of therake faces 52A, which correspond to the main gash faces 17 of the firstthrough fourth embodiments, are formed so as to extend away via the stepportions 19, 20, and 21 from the rakes faces 52A only in the vicinity ofthe corner cutting edges 58 of the rake faces 52B within a range wherebythey do not reach the inner edges 59B. In this structure, the cornercutting edges 58 are formed so as to be continuous with the outercircumferential side of the end cutting edges 56 from the distal end tothe outer circumference of the sub gash faces 18.

Accordingly, according to a radius end mill in which component elementsof the first through fourth embodiments are combined with componentelements of the fifth through seventh embodiments, chips that are easilydisposed of by being curled or fragmented by the step portions 19, 20,and 21 of the first through fourth embodiments may be discharged easilyby the inner edges 59A, 59B, and 59C that are formed as single smoothlycontinuous convex curves of the fifth through seventh embodiments. As aresult, it is possible to achieve a further improvement in the chipprocessing performance.

INDUSTRIAL APPLICABILITY

The present invention relates to a radius end mill that is used forcutting work pieces such as, for example, metal dies.

According to the present invention, by forming a sub gash face, whichhas a larger angle of inclination with respect to the axis of the toolbody than that of the main gash face located on the innercircumferential side, on the outer circumferential side of the distalend portion of a wall surface that faces in the tool rotation directionof the chip discharge flutes, the corner cutting edge that is formed onthe distal end outer circumferential side ridge portion of this sub gashface may be provided with excellent sharpness, and it is possible,particularly when performing a cutting operation on the inclined face orcurved face of a metal die, to achieve efficient cutting by reducing thecutting resistance. Moreover, by making the step portions formed betweenthe sub gash faces and the main gash faces inclined faces that graduallyextend away as they move from the main gash face side to the sub gashface side, it is possible to prevent the chips from becoming blocked bythe step portions and to encourage a smooth chip discharge.

Moreover, by forming the inner edges of the rakes faces of the endcutting edges and the inner edges of the rake faces of the cornercutting edges as smoothly continuous single convex curves, according tothe present invention, it is possible to secure a large space fordischarging generated chips without any corner portions, where inneredges intersect with other, being formed, as is the case conventionally,and it becomes difficult for discharged chips to become caught. As aresult, an excellent chip discharge performance may be maintained.

1. A radius end mill in which end cutting edges and substantiallyarc-shaped corner cutting edges are formed on a tool body that isrotated around an axis, comprising: chip discharge flutes, which arehelically twisted, formed on an outer circumference of a distal endportion of the tool body; main gash faces whose angle of inclinationwith respect to the axis is a smaller angle than a twist angle of thechip discharge flutes, said main gash faces formed on innercircumferential sides of distal end portions of wall surfaces of thechip discharge flutes that face in a direction of rotation of the tool,the end cutting edges formed on a distal end of the main gash faces; andsub gash faces whose angle of inclination with respect to the axis hasbeen made greater than that of the main gash faces, said sub gash facesformed on an outer circumferential side of the main gash faces such thatthey extend away via step portions from the main gash faces, wherein thecorner cutting edges that have a protruding arc-shaped contour areformed so as to be continuous with an outer circumferential side of theend cutting edges from a distal end as far as an outer circumference ofthe sub gash faces.
 2. A radius end mill according to claim 1, whereinstep portions between the main gash faces and the sub gash faces areformed as inclined surfaces that move gradually away as they move fromthe main gash face side towards the sub gash face side.
 3. A radius endmill according to claim 2, wherein an angle of inclination of theinclined surfaces formed by the step portions is within a range of 30°to 60° with respect to a direction that is perpendicular to the sub gashfaces.
 4. A radius end mill according to claim 2, wherein the inclinedsurfaces are formed as concave curved surfaces.
 5. A radius end mill inwhich end cutting edges and substantially arc-shaped corner cuttingedges are formed on a tool body that is rotated around an axis, wherein:inner edges of rake faces of the end cutting edges and inner edges ofrake faces of the corner cutting edges are formed as a single, smoothlycontinuous convex curve.
 6. A radius end mill according to claim 5,wherein the rake face of the end cutting edge and the rake face of thecorner cutting edge are formed as a single, smoothly continuous curvedsurface.
 7. A radius end mill according to claim 5, wherein a ratio r/Dbetween a radius of curvature “r” of the substantially arc-shapedportions formed by the corner cutting edges and the diameter D of thetool body is set to 0.2 or more.
 8. A radius end mill according to claim5, wherein the radius of curvature “r” of the substantially arc-shapedportions formed by the corner cutting edges is set to (D−d)/2 or morefor the diameter D and the web thickness “d” of the tool body.
 9. A toolbody having a radius end mill in which end cutting edges andsubstantially arc-shaped corner cutting edges are formed on the toolbody that is rotated around an axis, comprising: chip discharge flutes,which are helically twisted, formed on an outer circumference of adistal end portion of the tool body; main gash faces whose angle ofinclination with respect to the axis is a smaller angle than a twistangle of the chip discharge flutes, said main gash faces formed on innercircumferential sides of distal end portions of wall surfaces of thechip discharge flutes that face in a direction of rotation of the tool,and the end cutting edges formed on a distal end of the main gash faces;and sub gash faces whose angle of inclination with respect to the axishas been made greater than that of the main gash faces, said sub gashfaces formed on an outer circumferential side of the main gash facessuch that they extend away via step portions from the main gash faces,and wherein the corner cutting edges that have a protruding arc-shapedcontour are formed to be continuous with an outer circumferential sideof the end cutting edges from a distal end as far as an outercircumference of the sub gash faces.
 10. A radius end mill according toclaim 9, wherein step portions between the main gash faces and the subgash faces are formed as inclined surfaces that move gradually away asthey move from the main gash face side towards the sub gash face side.11. A radius end mill according to claim 10, wherein an angle ofinclination of the inclined surfaces formed by the step portions iswithin a range of 30° to 60° with respect to a direction that isperpendicular to the sub gash faces.
 12. A radius end mill according toclaim 10, wherein the inclined surfaces are formed as concave curvedsurfaces.